Entanglement Drives Common Noise into the Strong-Coupling Regime

Abstract:Under Gaussian collective dephasing parallel to the signal, the superdecoherence of an $N$-atom Greenberger--Horne--Zeilinger (GHZ) state cancels its gain in Fisher information, so GHZ frequency sensitivity is limited to an atom-number-independent floor. We demonstrate that this floor is a property of Gaussian diffusion: a single common phase kick can at most randomize the phase of an $N$-atom coherence, so discrete events at rate $\Gamma$ cannot dephase any coherence order faster than $2\Gamma$. At the same single-atom coherence time, finite-rate Poisson kicks with an absolutely continuous amplitude law therefore saturate the order-$N$ decay rate and restore Heisenberg scaling. We prove that Gaussian diffusion is the worst case for GHZ and Dicke-cat probes under this calibration, that only the Brownian component of Lévy phase noise sets the asymptotic floor, and that the $1/N$ exponent is optimal for parallel Ramsey protocols. These results identify the counting statistics of the common noise, rather than its spectrum, as the property that bounds superdecoherence.

arXiv:2607.02962 [quant-ph]

(or arXiv:2607.02962v2 [quant-ph] for this version)

https://doi.org/10.48550/arXiv.2607.02962 Focus to learn more arXiv-issued DOI via DataCite

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